An overhead travelling carriage is provided in a clean room or a common plant, warehouse, library, hospital, or the like. The overhead travelling carriage runs along a running rail provided near a ceiling of the building. The overhead travelling carriage conveys articles by elevating or lowering the platform. To elevate and lower the platform, it is possible to use hanging members such as belts, wires, or ropes to support three or four points on the platform.
The Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 2003-118972 proposes an elevate and lower driving section 80 such as the one shown in FIG. 6, and a pair of drums 82 is installed along each of three sides of an equilateral triangle so that the hanging members can be wound around and fed from the drums 82. An output from a driving motor 86 is transmitted to the drums arranged on the equilateral triangle, via a gearbox 84. The hanging members from the lateral pair of drums 82, 82 on each side of the equilateral triangle are connected to the same point on a platform (not shown in the drawing). As a result, the three points on the platform are each supported by the two hanging members. Thus, the platform is supported at the three points and can stably maintain its position. However, the elevate and lower driving section 80 must transmit the output from the running motor 86 to the drums arranged on the three sides of the equilateral triangle. This complicates a transmission mechanism such as the gearbox 84.
FIG. 7 shows a platform 90 that is an example of a 4-point support platform. 92 is a hanging member. In the elevate and lower driving section side, for example, a lateral pair of drums is utilized so that two hanging members 92 can be wound around and fed from each drum. This simplifies the structure of the elevate and lower driving section. However, it is difficult to uniformly impose the load of the platform on the four hanging members 92. Actually, any one of the hanging members 92 may become loose and may not be tensioned. Further, to allow the four hanging members 92 to support a load, it is necessary to accurately adjust the lengths of the hanging members 92 and the like. However, with the four hanging members 92, involving an extra one point compared to the three-point support configuration, it is very difficult to adjust the lengths of the hanging members 92 and the like. The hanging members 92 cannot be sufficiently adjusted simply by using the certain heights of the platform. As the feeding or winding of the hanging members 92 proceeds, the balance between the hanging members 92 may be lost. Thus, as the platform elevates or lowers, the tension is released from the hanging members 92 that have been tensioned, while instead the hanging members 92 that have not been tensioned are tensioned. This changes the positions of the three points at which the platform is supported, during elevating or lowering. Consequently, the position of the platform may change during elevating or lowering to vibrate the platform. As described above, no mechanisms are known which have accomplished both objects to prevent the vibration of the platform and to simplify the driving mechanism.